Magnetic thin film element, memory element using the same, and method for recording and reproducing using the memory element

ABSTRACT

A magnetic thin film element is provided with a magnetoresistive film including a first magnetic layer composed of a perpendicular magnetization film, a second magnetic layer composed of a perpendicular magnetization film having a higher coercive force than that of the first magnetic layer, and a nonmagenetic layer interposed between the first magnetic layer and the second magnetic layer. The resistance of the magnetoresistive film varies depending on whether or not the magnetic spins of the first magnetic layer and the second magnetic layer are in the same direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 09/794,499,filed Feb. 28, 2001, now U.S. Pat. No. 6,654,279 which is a divisionalof application Ser. No. 09/236,356, filed Jan. 25, 1999, now U.S. Pat.No. 6,219,275.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic thin film element making useof a giant magnetoresistive (GMR) effect, a memory element using themagnetic thin film element, and a method for recording and reproducingusing the memory element.

2. Description of the Related Art

Although a magnetic thin film memory is a solid-state memory with noactive part as is the case of a semiconductor memory, in the magneticthin film memory, information is not lost even if a power supply is cutoff, writing is enabled repeatedly up to an unlimited number of times,and there is no danger that the memory content may vanish with exposureto radiation, which are advantages in comparison with the semiconductormemory. In particular, recently, a thin film magnetic memory using thegiant magnetoresistive (GMR) effect is receiving attention because of alarger output in comparison with a conventional thin film magneticmemory using an anisotropic magnetoresistive effect.

For example, in the Journal of the Japan Society of Applied Magnetics(Vol. 20, P.22, 1996), a solid-state memory is disclosed, in which amemory element is fabricated by depositing a plurality of times astructure including a hard magnetic layer (HM), a nonmagnetic layer(NM), a soft magnetic layer (SM), and a nonmagnetic layer (NM).

FIG. 1 is a schematic sectional view showing a structure of such asolid-state memory. In the drawing, numeral 1 represents a hard magneticlayer, numeral 2 represents a nonmagnetic layer, and numeral 3represents a soft magnetic layer. In this solid-state memory, a senseline 4 is provided on both sides the magnetic film, and a word line 5 isprovided, and is isolated from the sense line 4 by an insulating layer6. An electric current is applied to the word lines 5 and the sense line4, and information is written means of the magnetic field generated as aresult.

Specifically, as shown in FIGS. 2A through 2D, by applying an electriccurrent to the word line 5, a magnetic field is generated in a differentdirection in response to the direction of electric current representedby numeral 7. The magnetization of the hard magnetic layer 1 is reversedby the magnetic field to record a memory in a state of “0” or “1”. InFIGS. 2A and 2C, the horizontal axis represents time T and the verticalaxis represents electric current I. In FIGS. 2B and 2D, the same membersas those in FIG. 1 are represented by the same numeral as in FIG. 1, anddetailed descriptions will be omitted.

For example, by applying a positive current, as shown in FIG. 2A, toproduce a rightward magnetic field, a memory state of “1” is recorded asshown in FIB. 2B. Also, by applying a negative current, as shown in FIG.2C, to produce a leftward magnetic field, a memory state of “0” isrecorded as shown in FIG. 2D.

In order to read information, as shown in FIGS. 3A through 3E, anelectric current 7 that is smaller than the recording current is appliedto the word line 5 to reverse the magnetization of the soft magneticlayer 3 only, and a resulting change in resistance is detected.

In FIG. 3A, the horizontal axis represents time T and the vertical axisrepresents electric current I. Also, in FIGS. 3B through 3E, the samemembers as those in FIG. 1 are represented by the same numeral as inFIG. 1, and detailed descriptions will be omitted.

When the giant magnetoresistive effect is used, resistance variesdepending on whether the magnetizations of the soft magnetic layer SMand the hard magnetic layer HM are parallel or antiparallel. Thus, amemory in a state of “1” can be discriminated from a memory in a stateof “0” in response to the change in resistance. For example, as shown inFIG. 3A, when a current is applied as a positive pulse and then anegative pulse, the magnetization of the soft magnetic layer 3 changesfrom rightward to leftward, and with respect to the memory in a state of“1”, a small resistance as shown in FIG. 3B is replaced by a largeresistance as shown in FIG. 3C. On the other hand, with respect to thememory in a state of “0”, a large resistance as shown in FIG. 3D isreplaced by a small resistance as shown in FIG. 3E. By detecting thechange in resistance as described above, information recorded in thehard magnetic layer HM can be read regardless of the magnetizationcondition of the soft magnetic layer SM after recording.

In the conventional magnetic thin-film memory having the structuredescribed above, however, as the area of the memory cell decreases, ademagnetizing field (self-demagnetizing field) generated in the magneticlayer increases so as to not be negligible, and the magnetizationdirection of the magnetic layer that stores records is no longer fixedin one direction, resulting in instability. Therefore, in theconventional magnetic thin-film memory, the refinement (reduction insize) of a on-bit cell and the stable storage of information areincompatible, and high integration is impossible.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the problems in theconventional art described above and to provide a magnetic thin filmelement in which instability of the magnetization can be prevented evenif the element is finely structured (very small).

It is another object of the present invention to provide a memoryelement which stores information with high stability and can be highlyintegrated.

In order to achieve the first object of the present invention, in oneaspect, a magnetic thin film element is provided with a magnetoresistivefilm which includes a first magnetic layer composed of a perpendicularmagnetization film, a second magnetic layer composed of a perpendicularmagnetization film having a higher coercive force than that of the firstmagnetic layer, and a nonmagnetic layer interposed between the firstmagnetic layer and the second magnetic layer. The resistance of themagnetoresistive film varies depending on whether or not the magneticspins of the first magnetic layer and the second magnetic layer are inthe same direction.

In the magnetic thin film element, the nonmagnetic layer may be composedof a good conductor or an insulator.

In order to achieve the second object of the present invention, inanother aspect, a memory element includes the magnetic thin film elementdescribed above and at least one write line composed of a good conductorprovided in the vicinity of the magnetoresistive film of the magneticthin film element with an insulator therebetween.

In the memory element described above, a plurality of write lines may beprovided on the sides of the magnetoresistive film. In the memoryelement, information may be retained in response to the direction of themagnetic spin of the first magnetic layer, and the direction of themagnetic spin of the second magnetic layer may always be maintained inthe same direction. Alternatively, information may be retained inresponse to the direction of the magnetic spin of the second magneticlayer.

In still another aspect, a magnetic thin film memory, in accordance withthe present invention, includes a plurality of memory elements describedabove arrayed in a matrix on a substrate, and a magnetoresistive film ofeach memory element is electrically connected to a semiconductor devicecomposed of a field effect transistor or a diode.

In a further aspect, a method for recording using the memory element, inaccordance with the present invention, includes applying an electriccurrent to the write line, fixing a direction of the magnetic spin ofthe first magnetic layer by means of a magnetic field generated by theelectric current, and changing the direction of the electric current tobe applied to the write line to record a memory state of “0” or “1”.

In a still further aspect, a method for reproducing using the memoryelement, in accordance with the present invention, includes detectingresistance of the magnetoresistive film to reproduce informationrecorded as the direction of the magnetic spin in the first magneticlayer.

In a yet further aspect, a method for recording using the memoryelement, in accordance with the present invention, includes applying anelectric current to the write line, fixing a direction of the magneticspin of the second magnetic layer by means of a magnetic field generatedby the electric current, and changing the direction of the electriccurrent to be applied to the write line to record a memory state of “0”or “1”.

In a yet further aspect, a method for reproducing using the memoryelement, in accordance with the present invention, includes applying anelectric current to the write line, and using a change in resistanceresulting from the reversal of the magnetic spin of the first magneticlayer caused by a magnetic field generated by the electric current toreproduce information recorded in the second magnetic layer.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a structure of aconventional magnetic thin film memory element;

FIGS. 2A through 2D are diagrams which illustrate the recording ofinformation in a conventional magnetic thin film memory element;

FIGS. 3A through 3E are diagrams which illustrate the reproducing ofinformation in a conventional magnetic thin film memory element;

FIGS. 4A and 4B are schematic sectional views showing a structure of amagnetic thin film element in accordance with the present invention;

FIGS. 5A and 5B are diagrams which illustrate the magnetization of amagnetic thin film element in accordance with the present invention;

FIG. 6 is a schematic sectional view showing a structure of a memoryelement in accordance with the present invention, in which the magneticthin film element shown in FIGS. 4A and 4B is used;

FIG. 7 is a schematic sectional view showing another structure of amemory element in accordance with the present invention, in which themagnetic thin film element shown in FIGS. 4A and 4B is used;

FIGS. 8A through 8D are diagrams which illustrate the magnetization of amemory element in accordance with the present invention;

FIG. 9 is a schematic sectional view of a memory cell using a memoryelement in accordance with the present invention; and

FIG. 10 is a schematic sectional view of another memory cell using amemory element in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in detail with reference to thedrawings.

Embodiment 1

FIGS. 4A and 4B are schematic sectional views showing a structure of amagnetic thin film element in accordance with the present invention.Numeral 11 represents a first magnetic layer composed of a perpendicularmagnetization film, numeral 12 represents a second magnetic layercomposed of a perpendicular magnetization film having a higher coerciveforce at room temperature in comparison with the first magnetic layer11, and numeral 13 represents a nonmagnetic layer. The first magneticlayer 11 is deposited on the second magnetic layer 12 with thenonmagnetic layer 13 therebetween. The arrows represent magnetizationdirection, in particular, a direction of the spin constituting themagnetization. In FIG. 4A, the magnetic spin directions of the firstmagnetic layer 11 and the second magnetic layer 12 are parallel, and inFIG. 4B, they are antiparallel.

Materials for the first magnetic layer 11 and the second magnetic layer12 include magnetic materials exhibiting perpendicular magnetizationsuch as a ferrimagnetic film that is an alloy of a rare earth elementand a transition element of the iron group (RE/TM), a garnet film thatis an oxide magnetic film, an artificial lattice film of a rare earthelement and a transition metal of the iron group (RE/TM), PtCo, andPdCo.

As a RE-TM material, GdFe, GdFeCo, TbFe, TbFeCo, DyFe, DyFeCo, or thelike is preferably used because of an easy exhibition of perpendicularmagnetization. Among the magnetic films mentioned above, GdFe or GdFeCois more preferable as a material for the first magnetic layer 11 becauseits coercive force can be decreased. Although, as a material for thesecond magnetic layer 12, TbFe, TbFeCo, DyFe, DyFeCo, or the like ispreferably used because its coercive force can be increased, when thereversal of coercive force can be increased, when the reversal ofmagnetization is caused by a magnetic field generated by an electriccurrent, the required electric current value may be excessively largebecause of the excessively high coercive force in those materials, andthus, by using GdFe, GdFeCo, or the like, the composition is adjusted sothat the second magnetic layer 12 has a larger coercive force than thatof the first magnetic layer 11.

In the magnetic thin film element of the present invention, resistancevaries depending on whether the spin directions of the first magneticlayer 11 and the second magnetic layer 12 are parallel or antiparallel.For example, as shown in FIG. 4A, when the directions of the spins ofthe first magnetic layer i1 and the second magnetic layer. 12 areparallel, resistance is low, and as shown in FIG. 4B, when the spindirections of the first magnetic layer 11 and the second magnetic layer12 are antiparallel, resistance is high.

Further description will be made with reference to FIGS. 5A and 5B,using a RE-TM material. In FIGS. 5A and 5B, the same members as those inFIGS. 4A and 4B are represented by the same numerals as in FIGS. 4A and4B, and detailed n descriptions will be omitted.

In FIGS. 5A and 5B the outlined arrows represent a net magnetizationdirection RM, which corresponds to a difference in magnetization betweena rare earth element and an element of the iron group, and the blackarrows represent a magnetization direction IM of a transition element ofthe iron group. When the magnetic film is a ferrimagnetic film composedof a rare earth element and a transition element of the iron group, thesub-lattice magnetizations of the individual elements are antiparallel.The magnetization of the rare earth element is caused by 4f electrons.However, since the 4f electrons are deep within an inner shell, they donot greatly contribute to electric conductivity. On the other hand, someof the 3d electrons which contribute to the magnetization of thetransition element of the iron group are conduction electrons becausethey are near an outer shell. Therefore, magneto-resistance depending ona difference in spin direction is more easily influenced by the spin ofthe transition element of the iron group. Accordingly, the spindirection caused by magneto-resistance depends on the spin direction ofthe element of the iron group. For example, as shown in FIG. 5A, whenthe magnetic moment of the element of the iron group of the firstmagnetic layer 11 is parallel to that of the second magnetic layer 12,resistance is small, and as shown in FIG. 5B, when antiparallel,resistance is large.

Although, in FIGS. 5A and 5B, the transition element of theiron-group-rich (TM-rich) structure is used, in which the netmagnetizations of the individual magnetic layers and the magnetizationof the element of the iron group are in the same direction, otherstructures may be used, for example, a structure in which the firstmagnetic layer 11 is rare-earth-element-rich (RE-rich) and the secondmagnetic n layer 12 is TM rich, or vice versa.

Since the magnetic thin film element in the present invention iscomposed of a perpendicular magnetization film, in comparison with anelement composed of an in-plane magnetization film, there is a largedifference in stability of the magnetization when the element is finelystructured. Specifically, when an element is composed of a knownmagnetoresistive film such as NiFe/Cu/Co, an amount of saturationmagnetization is approximately 800 emu/cc or more, and if the width ofthe element is in the submicron range, a demagnetizing field increasesbecause magnetic poles on the ends of the film move closer to oneanother, and thus, the spins rotate at the film ends and are alignedparallel to the ends. On the contrary, in a perpendicular magnetizationfilm, the amount of demagnetizing energy is smaller than a Pperpendicular magnetic anisotropy constant, and therefore, the amount ofsaturation magnetization is suppressed at approximately 300 emu/cc orless at the maximum. Even if the width of the element is decreased, themagnetic poles on the “ends” of the film do not move closer to oneanother, and the demagnetizing field does not increase. Accordingly,even at a submicron width, magnetization can be maintained sufficientlystably. Therefore, when the element is used for a,memory element, theintegration can be significantly enhanced.

Embodiment 2

A magnetic thin film element of this embodiment has the structure shownin FIGS. 4A and 4B, and a nonmagnetic layer 13 interposed between afirst magnetic layer 11 and a second magnetic layer 12 is composed of agood conductor. This element is hereinafter referred to as a spinscattering element. A good conductor preferably has higher conductivitythan that of the first magnetic layer 11 or the second magnetic layer12, and, for example, Cu may be used.

Since a good conductor having Cu as a major constituent has its Fermienergy close to that of the magnetic layer and has good adhesion,resistance easily occurs at the interface when the magnetizationdirection changes, and thus a large magneto-resistance ratio can beobtained. Also, preferably, the nonmagnetic layer has a thickness of 5 Åto 60 Å.

Preferably, by providing a magnetic layer having Co as a majorconstituent, between the first magnetic layer 11 and the nonmagneticlayer 13, or between the second magnetic layer 12 and the nonmagneticlayer 13, or both between the first magnetic layer 11 and thenonmagnetic layer 13 and between the second magnetic layer 12 and thenonmagnetic layer 13, a magneto-resistance ratio is increased, resultingin a higher S/N ratio. In such a case, the layer having Co as a majorconstituent preferably has a thickness of 5 Å to 20 Å.

The thickness of the first magnetic layer 11 must be set so that a giantmagnetoresistive effect is efficiently produced. Specifically, if thethickness of the first magnetic layer 11 greatly exceeds a mean freepath of electrons, the effect decreases because of phonon scattering,and thus the thickness is preferably 200 Å or less, and more preferably150 Å or less. However, if the first magnetic layer 11 is excessivelythin, resistance of the cell decreases, resulting in a decrease inoutput of playback signals as well as difficulty in retaining themagnetization, Therefore, the thickness of the first magnetic layer 11is preferably 20 Å or more, and more preferably 80 Å or more.

Since the thickness of the second magnetic layer 12 is set so that agiant magnetoresistive effect is efficiently produced, the same as thefirst magnetic layer 11, the thickness is preferably 200 Å or less, andmore preferably 150 Å or less. However, if the thickness is excessivelysmall, resistance of the cell decreases, resulting in a decrease inoutput of playback signals as well as difficulty in retaining themagnetization. Therefore, the thickness of the second magnetic layer 12is preferably 20 Å or more, and more preferably 80 Å or more.

In order to improve a S/N ratio, a unit including a first magneticlayer, a nonmagnetic layer, a second magnetic layer and a nonmagneticlayer may be deposited a plurality of times. As the number of units tobe deposited increases, a magneto-resistance ratio increases, which ispreferable. However, if the number is excessively large, the thicknessof the magnetoresistive film increases and a large volume of electriccurrent is required. Therefore, the number of units to be deposited ispreferably 40 or less, and more preferably approximately 3 to 20.

Embodiment 3

A magnetic thin film element of this embodiment has the structure shownin FIGS. 4A and 4B, and a nonmagnetic layer 13 interposed between afirst magnetic layer 11 and a second magnetic layer 12 is composed of aninsulator, and thus a spin-tunnel film is formed. When an electriccurrent is applied perpendicular to the film surface during reproducing,tunneling of electrons from the first magnetic layer 11 to the secondmagnetic layer 12 occurs.

Since such a spin-tunnel element has a higher magnetoresistance ratio incomparison with the spin scattering element described above, outputsignals having a satisfactory S/N ratio can be obtained.

In the spin-tunnel magnetic thin film memory element of this embodiment,a ferromagnetic tunnel junction, which includes a ferromagneticmaterial, an insulator, and a ferromagnetic material, is formed. Sinceconduction electrons of the ferromagnetic materials tunnel whilemaintaining the spins, tunnel probability varies depending on themagnetization condition of both magnetic layers, resulting in a changein tunnel resistance. Accordingly, when the magnetizations of the firstmagnetic layer 11 and the second magnetic layer 12 are parallel,resistance is small, and when the magnetizations of the first magneticlayer 11 and the second magnetic layer 12 are antiparallel, resistanceis large. As the difference in density of states between upward spinsand downward spins increases, the resistance increases, resulting inlarger output signals. Thus, a magnetic material having high spinpolarizability is preferably used for the first magnetic layer 11 andthe second magnetic layer 12. Specifically, with respect to the firstmagnetic layer 11 and the second magnetic layer 12, Fe, which has highpolarizability of upward and downward spins at the Fermi surface, isselected as a major constituent, and Co is selected as a secondconstituent.

The thickness of the magnetic thin film element of this embodiment ispreferably from 100 Å to 5,000 Å.The reason for this is that, firstly,when an oxide is used as the insulator, since magnetism at the interfacebetween the magnetic layer and the oxide is weakened under the influenceof the oxide, the portion with weakened magnetism dominates in theentire film if the thickness is small, resulting in an adverse effect onthe magnetism of the film. Secondly, when a memory element is refined tothe submicron range, since the volumes of the first magnetic layer 11and the second magnetic layer 12 decrease, perpendicular magneticanisotropic energy decreases, resulting in a decrease in themagnetization retention function of the individual layers. Also, if thethickness is excessively large, resistance of the cell increasesexcessively. Thus, the thickness is preferably 5,000 Å or less, and morepreferably, 1,000 Å or less.

As described above, since the magnetic thin film element of thisembodiment uses the magnetoresistive effect by spin-tunneling, thenonmagnetic layer 13 must be an insulating layer so that electronstunnel while retaining their spins. The nonmagnetic layer 13 may beentirely insulating, or may be partially insulating. An example in whichan oxide layer composed of an oxidized nonmagnetic metal film is used asthe nonmagnetic layer 13 includes an Al₂O₃, layer formed by oxidizing aportion of an Al film in air or in a vacuum by plasma oxidation. Otherexamples are aluminum nitride (AlNx), silicon oxide (SiOx), siliconnitride (SiNx), and nickel oxide (NiOx). Preferably, aluminum oxide(AlOx) is used. Also, in order to cause spin-tunneling, an appropriatepotential barrier is required to the energy of conduction electrons ofthe first and the second magnetic layers. The materials mentioned aboverelatively easily produce the barrier, which is advantageous inproduction.

Preferably, the nonmagnetic layer 13 is a uniform layer having athickness of approximately several tens of Å, and the thickness of itsinsulating portion has a thickness from 5 Å to 30 Å. If the thickness isless than 5 Å, there is a possibility of an electrical short circuitbetween the first magnetic layer 11 and the second magnetic layer 12. Ifthe thickness is more than 30 Å, tunneling of electrons does not easilyoccur. More preferably, the thickness is 5 Å to 25 Å, and still morepreferably, the thickness is 6 Å to 18 Å.

Embodiment 4

One of the applications of a magnetic thin film element in accordancewith the present invention is an application to a memory element, whichrecords information of “0” or “1” in response to the magnetizationdirection, and reads information using a difference in resistance.

FIG. 6 is a schematic sectional view showing a memory element which usesthe magnetic thin film element described above. In FIG. 6, the samemembers as those in FIGS. 4A and 4B are represented by the same numeralsas in FIGS. 4A and 4B, and detailed descriptions will be omitted.Numeral 14 represents the magnetic thin film element shown in FIGS. 4Aand 4B, numeral 15 represents a write line composed of a good conductor,and numeral 16 represents a magnetic field generated by applying anelectric current to the write line 15.

In the memory element of this embodiment, magnetization information “0”or “1” is recorded in response to the spin direction, i.e., upward ordownward, of either the first magnetic layer 11 or the second magneticlayer 12. Whether information is stored in the first magnetic layer 11or in the second magnetic layer 12 depends on a structure of the elementwhich will be described below. In the memory element of this embodiment,recording is performed by applying an electric current to the write line15 placed in the vicinity of the first and second magnetic layers 11 and12, and reversing the magnetization of the first magnetic layer 11 orthe second magnetic layer 12 by means of the magnetic field 16generated. Although, in FIG. 6, an electric current is applied toward(into) the drawing, if the electric current is applied in the reversedirection, a reversed magnetic field is generated and the direction ofthe spin can be reversed. Whether information is recorded in the firstmagnetic layer 11 or in the second magnetic layer 12 depends on a mediumtype as described below. An insulating film (not shown in the drawing)is provided between the write line 15 and the magnetoresistive film 14.The insulating film is provided in order to prevent the write line 15and the magnetoresistive film 14 from being electrically connected toeach other. The deterioration of playback signals caused by the leakageof an electric current applied to the, magnetic thin film element to thewrite line 15 can thus be prevented.

The magnetoresistive film 14 exhibits low resistance when the spin ofthe first magnetic layer 11 and the spin of the second magnetic layer 12are parallel, and exhibits high resistance when they are antiparallel.Therefore, digital information recorded can be detected by detecting theresistance of the magnetoresistive film, or a change in the resistance,as described below.

The write line 15 is set so that a magnetic field is generatedperpendicular to the magnetoresistive film 14 by applying an electriccurrent. For that purpose, the write line 15 is preferably placed sothat an electric current is applied parallel to the film surface. Also,when the space between the write line 15 and the magnetoresistive film14 is large, a sufficient magnetic field cannot be applied, and when thespace is too narrow, a dielectric breakdown may occur, or a tunnelcurrent may flow. Accordingly, the space is at least from 10 Å to 1 μm,and preferably, from 50 Å to 1,000 Å.

Embodiment 5

A magnetic thin film memory element of this embodiment has the structureshown in FIG. 6, and includes a memory layer (first magnetic layer 11),a nonmagnetic layer 13, and a pinned layer (second magnetic layer 12).In the magnetic thin film memory element, the first magnetic layer 11 isa memory layer for storing magnetic information, and the second magneticlayer 12 is a pinned layer in which the magnetization is always alignedin a predetermined direction in any state (i.e., storing, recording, andreproducing). A method of recording will be described with reference toFIGS. 4A and 4B. Data of “0” and “1” are set to correspond to upwardmagnetization of the first magnetic layer 11 (FIG. 4A) and downwardmagnetization (FIG. 4B), respectively. As described above, forrecording, the magnetization of the first magnetic layer 11 is reversedby a magnetic field generated by an electric current applied to a writeline 15. In such a manner, since resistance is low in a state of “0” andresistance is high in a state of “1”, during reproducing, informationcan be detected from the absolute value of resistence, without reversingthe magnetization of the magnetic layer. Therefore, the reversal of themagnetization is not required to detect a change in resistance duringreproducing, and reproducing can be performed quickly and with lowcurrent consumption.

Although the spin direction of the second magnetic layer 12 is upward inthe above description, it may be downward. Also, data of “0” and “1” maybe set to correspond to downward magnetization of the first magneticlayer 11 and upward magnetization, respectively.

Although, as magnetic materials for the first magnetic layer 11 and thesecond magnetic layer 12, the RE-TM materials described above may beused, with respect to the second magnetic layer 12 as the pinned layer,TbFe, TbFeCo, DyFe, DyFeCo, or the like having a high coercive force ispreferably used. Additionally, providing an anti ferromagnetic materialsuch as FeMn, IrMn, or NiO on the second magnetic layer 12 on the sideopposite to the interface with the nonmagnetic layer will increase thecoercive force of the second magnetic layer 12.

If the coercive force of the first magnetic layer 11 is too low, memorycharacteristics deteriorate, and if it is too high, recording currentincreases. Accordingly, the coercive force of the first magnetic layer11 is preferably from 5 Oe to 50 Oe. If the coercive force of the secondmagnetic layer 12 is too low, there is a possibility of reversal of themagnetization during recording and reproducing, and if it is too high,it is difficult to perform initialization in which the spin is alignedin one direction. Accordingly, the coercive force of the second magneticlayer 12 is preferably from 20 Oe to 20 kOe. Also, the coercive force ofthe first magnetic layer 11 is preferably set at approximately half ofthat of the second magnetic layer 12.

Embodiment 6

A magnetic thin film memory element of this embodiment has the structureshown in FIG. 6, and includes a detection layer (first magnetic layer11), a nonmagnetic layer 13, and a memory layer (second magnetic layer12). In the magnetic thin film memory element, the second magnetic layer12 is a memory layer for storing magnetic information, and the firstmagnetic layer 11 having a small coercive force is provided for readingthe magnetic information stored in the second magnetic layer 12 using amagnetoresistive effect. FIGS. 8A through 8D illustrate themagnetization of such a magnetic thin film memory element duringrecording and reproducing. In FIGS. 8A through 8D, the same members asthose in FIGS. 4A and 4B are represented by the same numerals as inFIGS. 4A and 4H, and detailed descriptions will be omitted. The arrowsrepresent the direction of the magnetic spin of the individual magneticlayers.

In this embodiment, data of “0” and “1” are set to correspond to upwardmagnetization of the second magnetic layer 12 (FIG. 8A) and downwardmagnetization (FIG. 8B), respectively. For recording, the magnetizationof the second magnetic layer 12 is reversed by a magnetic fieldgenerated by recording current.

For reproducing, an electric current which is weaker than that duringrecording is applied to a write line, or, as described below, anelectric current is applied to only one of two write lines provided, togenerate a magnetic field which is smaller than that during recording,and the magnetization of the detection layer, only, is reversed, withoutreversing the magnetization of the memory layer. For example, when “0”is recorded, the magnetization is changed from a state shown in FIG. 8Ato a state shown in FIG. 8C, or the reverse. When “1” is recorded, themagnetization is changed from a state shown in FIG. 8B to a state shownin FIG. 8D, or in reverse. Resistance changes from low to high in thecase of “0”, and changes from high to low in the case of “1”. Thus,recorded information can be detected by a change in resistance. In thismethod, even a minute change in signals can be detected usingdifferential detection or the like, in comparison with the method ofdetecting the absolute value of resistance, and thus, reproducing can beperformed with high detectivity.

Additionally, data of “0” and “1” may be set to correspond to downwardmagnetization of the second magnetic layer 12 and upward magnetization,respectively.

Although, as :magnetic materials for the first magnetic layer 11 and thesecond magnetic layer 12, the RE-TM materials described above may beused, since the magnetization of both layers is reversed duringrecording and reproducing, GdFe, GdFeCo, or the like having a lowercoercive force is preferably used.

If the coercive force of the first magnetic layer 11 is too low,playback signals deteriorate, and if it is too high, regenerativecurrent increases. Accordingly, the coercive force of the first magneticlayer 11 is preferably from 2 Oe to 20 Oe. If the coercive force of thesecond magnetic layer 12 is too low, memory characteristics deteriorate,and if it is too high, recording current increases. Accordingly, thecoercive force of the second magnetic layer 12 is preferably from 5 Oeto 50 Oe. Also, the coercive force of the first magnetic layer 11 ispreferably set at approximately half of that of the second magneticlayer 12.

Embodiment 7

If two or more write lines are placed in the vicinity of amagnetoresistive film 14 as shown in FIG. 7, magnetic fields generatedby the individual write lines are added, enabling the generation of alarger magnetic field. In FIG. 7, numeral 14 represents the magneticthin film element shown in FIGS. 4A and 4B, numerals 17 and 18 are writelines composed of a good conductor, and numerals 19 and 20 are magneticfields generated by applying an electric current to the write lines 17and 18, respectively.

In the structure including a detection layer (first magnetic layer 11),a nonmagnetic layer 13, and a memory layer (second magnetic layer 12), aweaker magnetic field is generated during reproducing in comparison withduring recording. Therefore, by applying an electric current to onewrite line during reproducing and by applying an electric current to twowrite lines during recording, a current margin between reproducing andrecording can be increased, resulting in the stable operation with norecording errors during reproducing.

Embodiment 8

When one memory chip has a capacity of several hundreds of megabytes orseveral gigabytes, a plurality of one-bit memory cells includingmagnetic thin film elements in accordance with the present invention arearrayed in a matrix to constitute the entire memory. In such a case,since reading is performed independently for each cell, if a write lineand a selector transistor are provided on each cell, integrationdecreases. Thus, a common write line is preferably provided on aplurality of cells.

However, in such a structure, when an electric current is applied to thewrite line, a magnetic field is applied to a plurality of memory cellsat the same time. Therefore, it is required to make a structure in whichthe magnetization of one memory cell, only, can be reversed, forexample, by applying an electric current to the memory cell to berecorded. For that purpose, an active element such as a field effecttransistor may be used for applying an electric current independently toa memory cell during reproducing. Thus, an electric current can beapplied selectively to one memory cell among many memory cells in thevicinity of the write line. Since the electric current path can be thesame as that used for reproducing and is perpendicular to an electriccurrent applied to the write line, the magnetic field generated by theelectric current is perpendicular to the magnetic field generated by thewrite line, and thus, the memory cell selected by the active element hasapplied to it, a larger resultant magnetic field in comparison withother memory cells, resulting in reversal of magnetization.

FIGS. 9 and 10 illustrate such memory cells in which one end of amagnetic thin film element is connected to a transistor and the otherend is connected to a source voltage VDD. In FIG. 9, numeral 21represents a magnetic thin film element, numerals 22 and 23 representwrite lines, numeral 24 represents a transistor, and numeral 25represents a control gate. In FIG. 10, numeral 31 represents a magneticthin film element, numerals 32 and 33 represent write lines, numeral 34represents a transistor, and numeral 35 represents a control gate.Although not shown in FIG. 9 or 10, a read line composed of a goodconductor is connected to the end of the magnetoresistive film 21 or 31,and a sense circuit or the like is connected so that a change inresistance can be detected. Write lines 22, 23, 32, and 33 are providedin the vicinity of the magnetoresistive films 21 and 31 with aninsulator composed of SiO₂, SiNx or the like therebetween. The writelines are placed perpendicular to the drawing and are used for writingto other memory cells (not shown in the drawing). The reproducingelectric current path is horizontal in FIG. 9, and vertical in FIG. 10.In the spin-tunnel element, the structure as shown in FIG. 10 isadopted. Although, in the spin scattering element, either structure maybe adopted, preferably the structure as shown in FIG. 9, in which theelectric current is applied horizontally, is used since the absolutevalue of resistance decreases in the structure as shown in FIG. 10 inwhich the electric current is applied perpendicular to the film surface.

Also, with respect to the structure including a detection layer (firstmagnetic layer), a nonmagnetic layer, and a memory layer (secondmagnetic layer), during reproducing, the magnetization of the detectionlayer can be reversed by applying a magnetic field to the magnetic thinfilm element of a specific memory cell in the same manner as duringrecording. Thus, a change in resistance occurs and the change isamplified by the sense circuit to be detected. In such a manner,information in a specific memory cell among many memory cells can beread.

Also, with respect to the structure including a memory layer (firstmagnetic layer), a nonmagnetic layer, and a pinned layer (secondmagnetic layer), since the absolute value of resistance is detected, theresistance of the element selected by the active element is amplified bythe sense circuit for detection.

Additionally, the magnetic thin film element and the magnetic thin filmmemory element described in the embodiments may be used for a magneticsensor, or a magnetic head of a hard disk or the like.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

1. A magnetic memory comprising a magnetoresistive film comprising: afirst magnetic layer comprising a perpendicular magnetization film; asecond magnetic layer comprising a perpendicular magnetization filmhaving a higher coercive force than that of said first magnetic layer; anonmagnetic layer arranged between said first magnetic layer and saidsecond magnetic layer; a switch element connected to said first magneticlayer or said second magnetic layer; a plurality of write lines arrangedin parallel to each other in the vicinity of the magnetoresistive film;and a periphery of the write lines surrounded by an insulator.